Hind sight Topic: CG discussions for IC/E power

[Howard Rush]

I think we're letting him use too many walnut shells for that one pea.

[RC Storick]

Humm only 3.12 oz of fuel? Do-ah! Also if my battery weight includes the wire and deans (which it does) Include tank weight and plumbing too along with at least 6.5 oz of fuel. SO as just a guess instead of the 3.1 figure its closer to 8.5-9 Not that is makes any difference but it would be nice to see the numbers.

[RandySmith]

Humm only 3.12 oz of fuel?

That is correct, the fuel load gets less as you fly, It only has 5.5 ounces in it in the pits  fueled up, the minute I crank it it gets lighter with each passing second.
If you want to be accurate you will average the fuel load, which is what i did, that is where the 3.12 comes from

Also if you want to be accurate.. The way people here are measuring where the CG is on the planes is apples and oranges. ie ..If you want it to be correct you will need to measure the CG on the IC planes with the fuel loaded, (then to be accurate you would average this distance and put it back 1/2 of the distance to the CG. )  this is where the CG really is... compared to the ELC  planes with the battery installed. This will result in giving the  IC plane even better number on Howards calc scale of inertia.

Please do not try to tell me the CG is not farther forward on an IC ship when you are actually flying it..and that is the "only"  place is matters... measuring the CG  with 5 to 9 ounces missing  would be the near the same as measuring the  CG of an ELC  plane  with the battery removed.

Randy

[RC Storick]

the tank empty weighs at least 1 oz and the plumbing weighs something. So your using 2 oz of fuel? Static CG is all hypothetical. Actual CG can only be read in flight. My CG is way forward. I thought this was about moment of inertia not CG

[RandySmith]

Humm only 3.12 oz of fuel? Do-ah! Alas if my battery weight includes the wire and deans (which it does) Include tank weight and plumbing too along with at least 6.5 oz of fuel. SO as just a guess instead of the 3.1 figure its closer to 8.5-9 Not that is makes any difference but it would be nice to see the numbers.

No not really  the Merlin  NEVER  EVER  EVER  uses more than 5 to 5.5 in my ships, and it will  never  use anywhere close to 8 ounces, the tank and 5 to 5.5 ounces of fuel  weighs  6.2 ounces.

I

[RC Storick]

No not really  the Merlin  NEVER  EVER  EVER  uses more than 5 to 5.5 in my ships, and it will  never  use anywhere close to 8 ounces, the tank and 5 to 5.5 ounces of fuel  weighs  6.2 ounces.

I

The figures Eric gives are for a 75 not a 40 and doesnt a 75 weigh more that 11.5? there is also a lot missing in his figures like the coupler and part of the pipe in front of the CG.  not that I even know what all this means. All I know is how my plane reacts. He is including the arming switch so at least you have to include the tubing and filter for .5 more.

[RandySmith]

the tank empty weighs at least 1 oz and the plumbing weighs something. So your using 2 oz of fuel? Static CG is all hypothetical. Actual CG can only be read in flight. My CG is way forward. I thought this was about moment of enurtha not CG

Lets  look at it this way   how much weight in fuel is in my tank when I am doing the square 8s, the  overheads?  the hour glass, it is much less than the 5 ounces i put in it.
This is  why you must average  the  weight of fuel.

Also you are take into consideration the CG on my plane is also forward when I fuel it up...  you fuel yours up by inserting a battery.

Also the  CG has a lot to do with the moment of inertia

one other thing, I can run my CG  even  farther  forward  by  using forward swept flaps..that also works on IC engines

and lastly even if I go back and use all the fuel load the numbers are still much better.

Randy

[RC Storick]

This discussion is all well and good. But I think the plane feels , turns and stops easier with the concentrated weight spread out over the legnth of the nose rather then in the first 6 inches. Not that my opinion matters but I like it. Now if they can just get the battery weight down some more.

[RandySmith]

The figures Eric gives are for a 75 not a 40 and doesnt a 75 weigh more that 11.5? there is also a lot missing in his figures like the coupler and part of the pipe in front of the CG.  not that I even know what all this means. All I know is how my plane reacts.

Yes you are correct Eric's number is light, but your number of 13 ounces is wrong, the Merlin 75 weighs 12.25 ounces  not 13, and the E Flite with the hardware and cables weighs more than 6.5

I can run his figures with the accurate weights if you like, it will change the numbers slightly,
Also you are looking at an E-25 and comparing to a PA  75 when you would have a much more accurate comparasion using and Aero Tiger 36.

or you could still use the 75 and use an EC motor that is more the power a 75 will put out, that will weigh 10.5 ounces.

I use a 40  and a 51 in my planes and they are both loafing and not using anywhere near the power you can get from them.
The 75 will turn a Rev UP  16 x 4.5 prop and will fly an orange Intrepid XL thru a pattern in a dead 4 cycle very easily.

There is  much apple and watermelon compares  I have seen on this.  I think most anyone would be better off  using real numbers...or better yet concentrate on your power system and not so much on other peoples power packages.

Randy

[RC Storick]

OK your right I'm wrong. I have weighed all the stuff less fuel and the IC package weighs more. I have done this on a scale not guessing

Does anyone think for a moment with as weight crazy as I am I would use the heaver set up? Again I am not saying electric is the best the jury is still out. But its looking good.

[RandySmith]

This discussion is all well and good. But I think the plane feels , turns and stops easier with the concentrated weight spread out over the legnth of the nose rather then in the first 6 inches. Not that my opinion matters but I like it. Now if they can just get the battery weight down some more.

I agree  with you..however  my power system is NOT concentrated in the first 6 inches, it is spread out over 9 inches , and my fuel is pushed back to the LE of the wings, most ELC  planes I see now have the fuel load pushed up very close to the motor, also the bulk of the weight of an ELC motor is farther foward than my IC motor by a lot.

Randy

[RC Storick]

Anyway you cut it a 6.5 engine on the nose ring is lighter than a 12 OZ engine in the same place. All I know is how it relates in the handle. Sure you can get the same thing with IC but directional stability diminishes as you move CG back. I am not the one who brought this up. I have both set ups and I like the IC as well. I am just experimenting with this too see if its going to suit me. Eric brought up the comparison.

[RandySmith]

Anyway you cut it a 6.5 engine on the nose ring is lighter than a 12 OZ engine in the same place. All I know is how it relates in the handle. Sure you can get the same thing with IC but directional stability diminishes as you move CG back

Yes But I can play that too,  a  10 ounce ELC motor mounted right up front on the nose ring weighs  more than a 8.2 ounce PA 40 mounted 2 inches back from the nose ring

That is a much more accurate compare than an E Flite 25 vs  PA 75 which is what your trying to say is even. it is not, the E Flite 25 would be much more close to a 7.9 ounce AT 36.

And if you want to talk about  CG location  you still have to rethink the way your doing it, or just measure your CG with the battery removed.

I just went downstairs and weighed 2 systems too, an IC and an ECL of equivalent power, the ECL weighed more.

All of this means very little when people are figuring number wrong  to try to get a better compare for what they are using.  You have to use  real figures and not bogus numbers

Randy

[RandySmith]

Anyway you cut it a 6.5 engine on the nose ring is lighter than a 12 OZ engine in the same place. All I know is how it relates in the handle. Sure you can get the same thing with IC but directional stability diminishes as you move CG back. I am not the one who brought this up. I have both set ups and I like the IC as well. I am just experimenting with this too see if its going to suit me. Eric brought up the comparison.

Yep  I like both also, and the only thing that really matters is how it works for you, and how you like it, the exercise that is going on for years now on people telling others  how much better  their system is, and your sucks  is  really counter productive, especially when bogus numbers are used and  other don't understand how this related to  moments of inertia. We would all be better off building and practicing more !

Randy

[RC Storick]

I have it on the scale right now motor with wires is 6.6 oz. I guess I will have to dig out my /75 and fill the tank and weigh The stuff all over. But if I remember correctly it was 3 oz heaver in the ready to run mode than the power 25 setup.

Yep  I like both also, and the only thing that really matters is how it works for you, and how you like it, the exercise that is going on for years now on people telling others  how much better  their system is, and your sucks  is  really counter productive, especially when bogus numbers are used and  other don't understand how this related to  moments of inertia. We would all be better off building and practicing more !

Randy

I agree! I like them both there is no comparison as far a torque to a 75.

[RandySmith]

I have it on the scale right now motor with wires is 6.6 oz. I guess I will have to dig out my /75 and fill the tank and weigh The stuff all over. But if I remember correctly it was 3 oz heaver in the ready to run mode than the power 25 setup.

I agree! I like them both there is no comparison as far a torque to a 75.

Yep which is why it will spin a 15 inch 3 or 4 blade or the 16.5 inch 2 blade with ease.

Again  so far as the  weights and the  power... you cannot compare a 75 PA  to a E25  not even remotely close, if you want to be close compare it to a 7.9  ounce AT 36, or even a PA 40 at 8.2 ounces which can put out more power.

Again I can compare my PA 51 to an  equilalent E Power motor that weighs 10 ounces and a much heavier battery pack that would be required for that motor.

I ran Eric;s  numbers with  more accurate figures on everything.

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                                                PA 75                                                                                                  E-25
            Moment (contribution to CG), inch-oz   221.4               Moment (contribution to CG), inch-oz   214.45         
            Moment of inertia about CG, inch2-ozm   2275.36               Moment of inertia about CG, inch2-ozm   2238.6   

Much closer but still is a total joke in comparing the 2 when a 7.9 or 8.2 ounce AT or PA  would be closer in power.      

[Eric Viglione]

Wow, you two have been busy... some of us need our beauty rest, heh...

Sorry about the numbers, I was going from memory on the 75...  and the 3.1 is not the fuel load silly, it's the weight of an empty magnum metal 8 ounce tank, including plumbing, fuel filter,etc. I was at work, and only spent a few minutes on the excersize.

It was such a joke to me, as Randy points out, comparing my largest IC package to one of the smaller EP packages, that I got sloppy and I apologize. It was close enough in my mind to make the obvious point, that whatever your feeling at the handle is more likely from building a nice light airplane and flying it with a small diameter prop than anything else...

If I really wanted to compare apples to apples I should have chosen the big 5s battery Plettenburg setup to really drive my point home... or gone and wieghed my little PA40 setup which is about right for your size plane... the only difference being, my little PA40 will still have enough power left to reliably pull a 74 ounce Patternmaster through the whole pattern and last for a thousand flights that way if I wanted, because it's within the 40's native tolerance, and the E25 setup as you spec'ed it with that battery, well... couldn't make it through the entire first flight without overheating and shutting down prematurely.

If your still going to throw stones at my numbers Sparky, here's a quote from respected website, fesselflug, for a plane more equivelent to my Katana in size & power:

"Target weight was based on a 63oz plane with 7oz of fuel. The Plettenburg Orbit 30-12 motor weighs 10.7oz (305gm), the Schulze 18.46k F2B ESC weighs 1.5oz.(45gm) The ThunderPower 5S2P 4200 Pro Lite battery weighs 16.7oz.(473gm) The AeroLectric timer-processor board weighs .75oz.(20gm)"

This is probably a more comparible package to a PA75... well, closer anyways. I don't have time to plug in the numbers into the sheet right now, I gotta go flying, but you can just see where this will go, even with Randy's more accurate PA75 numbers. Even at that, I'm still pretty sure this Plett still wouldnt spin the same props as a 75, Randy would know better than I, but it's a lot closer than the E25.

Have fun, as I'm sure the debate will continue in my absence...

EricV

[Mark Scarborough]

guys, its not about what prop the endine COULD swing, its about the prop you DO swing,, Random guess, you wont be flying your PA airplane with a 16 inch prop,,

the Eflight 25 setup ( with a 4S pack) is pretty capable of flying a lot of ST 60 sized airplanes,, its not weak by any stretch,, I flew the setup in a 72 oz airplane and while I am not an expert pilot,, I could tell I was not lacking power,,

remember,, it takes x amount of power to fly X airplane through the pattern,, having an abuncance beyond that certainly is great,, but it still only takes the same amount to perform,,,

That being what it is,, the eflight 25 in a 630 tyo 650 inch airplane in mid 60 oz area is a pretty solid combo,,

[RandySmith]

guys, its not about what prop the endine COULD swing, its about the prop you DO swing,, Random guess, you wont be flying your PA airplane with a 16 inch prop,,

the Eflight 25 setup ( with a 4S pack) is pretty capable of flying a lot of ST 60 sized airplanes,, its not weak by any stretch,, I flew the setup in a 72 oz airplane and while I am not an expert pilot,, I could tell I was not lacking power,,

remember,, it takes x amount of power to fly X airplane through the pattern,, having an abuncance beyond that certainly is great,, but it still only takes the same amount to perform,,,

That being what it is,, the eflight 25 in a 630 tyo 650 inch airplane in mid 60 oz area is a pretty solid combo,,

Hi Mark
No one said is wasn't
Power is about what prop it will turn and I do have one I fly with a 16.5 inch prop.  But you missed the point entirely, no one said you had to use any size prop, this was about the ridiculous compare or the PA 75 to the E25 as equals,, they are not
The AT 36 can and has flown 60 sized ships a TP for one, and it can fly even larger planes, The 8.2 ounce Merlin 40 will fly an Impact with ease, as It will turn the exact same prop people use on the VF40 faster.
The point was that the 7.9 or 8.2 ounce motor was more comparable in power than the 12.5 ounce motor.

Randy

[RC Storick]

This is all I was saying look close E= engine   F/B = fuel battery


IC  12.5 E  -------6.5 F/B-------->LE------CG =19 OZ

EP  6.5 E  -------12.5 F/B-------->LE------CG =19 OZ

Same weights just the the heavyest weight is closer to the CG. Concentrated weight is what sets up base line. This is not a debate about power or which on is better. Heck this has nothing to do with the title of this thread NOTHING.

[Eric Viglione]

Hi Sparky, You are quite right, this thread got a little out of hand really, heh heh.

1) It started about a couple missed opportunity at Brodaks, 1st, not wanting to fly the wing gear epower on grass, then not flying the second round flight with the backup IC plane because didn’t have 5% fuel handy and afraid it would run out early…
2) Then it went on to comparative power systems, and weather it would have happened with something else…
3) Then conclusions were made that not being prepared can and will happen no matter what power system you use, then
4) We went on to the advantages of less moments of inertia, and weather some power packages actually had that advantage or not, but
5) Then we found we couldn't compare moments of inertia of power packages without figuring out what was like for like because we were comparing an Epower system in a smaller plane to a the biggest IC in a larger plane...  blah blah blah…

Hahahahahahahahah! Talk about thread drift! Sorry Sparky! These things really do take on a life of their own!

Any who, it still boils down to personal preference, because most of the systems discussed can be designed or trimmed to at least a somewhat similar corner and feel at the handle if you are willing to do the work.
That assumes that any 2 pilots would like or want the same feel at the handle... which is a whole nother story.

You keep saying the heaviest parts on yours are closest to the C/G, and I keep trying to tell you the front mounted motors with all it's weight hanging on the spinner ring makes it a darn near wash, and well within the noise if you compare it to a comparable IC setup (not ideally my 75 and big Katana, say a 40 in a Staris would be a more apple to apple to your current bird). All you have to do is plug the numbers in the spread sheet and play with placement a little and you will see for yourself, If I move your 6.5 ounce motor back to where an IC engine bolts in, then wow, yes, you have a HUGE reduction in moment of inertia.

You like mechanic's terms, ok...Take a pencil and hold it by the pointy end. Put 2 pennies on the pencil a half inch back from the eraser. Remember how that feels pinched between your finger tips, thats the IC engine. Now remove those and take 1 penny and put it out on the eraser itself. Thats the EP. Its a wash. Like Derek said, we can feel the difference of a steel vs/aluminum lock nut on the prop because it's out at the very end of the moment.

Posturing and joking aside, I am truly VERY HAPPY for Sparky that he has a plane now that he really really likes, I know it's been a long and twisted road getting there for him, with many builds he's done since he put up this great forum. Sparky should be very proud that he’s done something not many of us can, and that is build a plane that came out as planned with the exact feel he wants.
I thought his P47 was the cat’s pajamas myself… it made the most visually pleasing corners I thought, regardless of what he was feeling at the handle. Wish I could finish half as nice as one of Sparky's too.

EricV

This is all I was saying look close E= engine   F/B = fuel battery


IC  12.5 E  -------6.5 F/B-------->LE------CG =19 OZ

EP  6.5 E  -------12.5 F/B-------->LE------CG =19 OZ

Same weights just the the heavyest weight is closer to the CG. Concentrated weight is what sets up base line. This is not a debate about power or which on is better. Heck this has nothing to do with the title of this thread NOTHING.

[RC Storick]

Electric is a diffrent animal. Everyone computes power to size. Well with Ep its not or at least not the motor. Power is in the battery. You just need a motor big enough to handle the power from the battery turning a specific prop to keep it from burning up. Took me a while to get this too.

[RandySmith]

This is all I was saying look close E= engine   F/B = fuel battery


IC  12.5 E  -------6.5 F/B-------->LE------CG =19 OZ

EP  6.5 E  -------12.5 F/B-------->LE------CG =19 OZ

Same weights just the the heavyest weight is closer to the CG. Concentrated weight is what sets up base line. This is not a debate about power or which on is better. Heck this has nothing to do with the title of this thread NOTHING.

Hi Sparky
I do know what your saying but...
What happens is this, it gets out of hand and people make wrong analogies and post wrong figures, In my case your nose moment is over an inch longer than mine, advantage me... your fuel weighs much more than my average 3 ounces, advantage me, I never have 6.5 ounces in my plane, and the fuel load gets lighter with each passing lap, you have to adjust for that, or take an average of the fuel.the CG figures must move outwards for yours. my fuel load is back against the rear bulkhead, many EC planes are showed much farther forward.

Also no one seem to want to mention the huge amount of lead in the front of some planes, this is concentrated weight too.
None of this can be argued if you want to try to cherry pick the largest motor, add more weight than it actually weighs, then compare it to the lightest motor you can run in EC.
The bottom line is the airplane design needs to be engineered to match the power train. Larger more powerful stabs and elevators neutralize the added weight to the front.. but IF you look at the inertia figures they are not near as far off as you think, and the lighter IC motor have better concentrated weight figures.
Concentrated weight does NOT only apply to the extreme nose of an airplane, it applies to the entire weight ahead of the CG.... Don't believe me?? concentrate a 25 ounce battery pack at 8 inches and see if it doesn't not make a difference over the 14 ounce battery pack.

Design the plane for the weights and loads it carries is WAY more important than just sticking a 6 ounce motor up front. that can cause its own troubles, as many have found out.

Randy

[Howard Rush]

Sparky should be very proud that he’s done something not many of us can, and that is build a plane that came out as planned with the exact feel he wants.

in one month!

[Howard Rush]

The point of posting that calculator was to show that for a given CG (moment of the stuff the same for both configurations), the configuration with the stuff closest together has the least moment of inertia.  That's because the moment of inertia contribution of each item increases with the square of distance from the CG.  An item a long way from the CG contributes way more moment of inertia than you'd think it oughta.  Try it.

You can indeed use-- and I did-- a calculation like this to figure out where to put the electric stuff when making an electric version of an IC airplane for which you know the location of engine, tank, pipe, and such.  But you really should figure on a lighter structure and prop for the electric, and it's been lots of folks' experience that the electric CG should be half an inch to an inch forward of the IC CG.  So it gets kinda complicated.

My personal experience has been that the electric stuff is heavier than the IC stuff, and that I've been able to get it to work vastly better than I could ever get the IC stuff to work.  

[Chris Wilson]

Never thought of that!  Sure, just move the Battery back beneath the Bellcrank where the CG is located! 

Damn!   Just tried that and now the CG isn't at the BC mount anymore.  Is that OK?  Should I fly it anyway?  Will it fly better now?  What'd I do wrong?

Ted

Hi Ted,
        when I said -
"concentrating the mass around the CG gives far more design flexibility and 'should' result in eventually a better model," you go on to say that you tried it and yet only moved mass rearward, and used that as a basis of criticism?

So I gather that you don't agree that centralizing the mass would be of benefit?

I do, and here we have the opportunity of using truly discreet components, with electric we can seriously use the greater mass of the fuel cell anywhere (within reason) as movable ballast (and this is what I truly got out of Roberts assertions) and that flexibility 'should' result in a better model.

So sure, just move the Battery back beneath the bell crank where the CG is located as long as the CG can be maintained by say perhaps reducing a corresponding amount of weight in the tail. (Just ruminating here outside of the above extreme example, keeping the moments intact and getting weight off the tail may be as simple as sacrificing looks and deleting anything further aft than the elevator hinge line except for the elevator itself of course.)

And how many models need lead in the tail to get the CG just right? Wouldn't it be nice to be able to keep both the lightest wing loading AND maintain the CG by simply shifting a necessary discreet component instead of adding a (possibly) unnecessary lump of lead?

And that is only covering pitch, what about using the battery mass to control roll for the vertical CG and tip weight?

Thanks.

[RandySmith]

"So sure, just move the Battery back beneath the bell crank where the CG is located as long as the CG can be maintained by say perhaps reducing a corresponding amount of weight in the tail. (Just ruminating here outside of the above extreme example, keeping the moments intact and getting weight off the tail may be as simple as sacrificing looks and deleting anything further aft than the elevator hinge line except for the elevator itself of course.) "


Sure you can do that, and instead of moving the nose moment for 10 to 11.5 inches, you can now move it out to 18 inches so the plane will balance.

Randy

[RandySmith]

"and it's been lots of folks' experience that the electric CG should be half an inch to an inch forward of the IC CG.  So it gets kinda complicated."

Hi Howard

Is this figured with a battery in the EC plane and  no fuel in the IC plane? or are you calculating the IC CG with fuel in it?  I am curious if they are not close to the same place when fueled.

Thanks
Randy

[Chris Wilson]

"So sure, just move the Battery back beneath the bell crank where the CG is located as long as the CG can be maintained by say perhaps reducing a corresponding amount of weight in the tail. (Just ruminating here outside of the above extreme example, keeping the moments intact and getting weight off the tail may be as simple as sacrificing looks and deleting anything further aft than the elevator hinge line except for the elevator itself of course.) "


Sure you can do that, and instead of moving the nose moment for 10 to 11.5 inches, you can now move it out to 18 inches so the plane will balance.

Randy

Hi Randy,
                I am talking about mass redistribution and the lessening of the moment of inertia not arm length.

If you 'could' reasonably redistribute the mass more around the CG without changing its location, and here the battery pack is a darn good start, would you not entertain a new model design to suit?

[Howard Rush]

"and it's been lots of folks' experience that the electric CG should be half an inch to an inch forward of the IC CG.  So it gets kinda complicated."

Hi Howard

Is this figured with a battery in the EC plane and  no fuel in the IC plane? or are you calculating the IC CG with fuel in it?  I am curious if they are not close to the same place when fueled.

I used half a tank of fuel in the IC plane and a battery in the electric.  For 4 oz. of fuel to move the CG of a 64-oz. airplane an inch, the center of the tank would have to be 16" forward of the new CG, wouldn't it?

[RandySmith]

Hi Randy,
                I am talking about mass redistribution and the lessening of the moment of inertia not arm length.

If you 'could' reasonably redistribute the mass more around the CG without changing its location, and here the battery pack is a darn good start, would you not entertain a new model design to suit?

Chris
Do you realize how very very short the tail moment would have to be if you moved the battery into the wing and moved the el motor back?

I think it would be a very funny looking stunt plane..unless you added lead ballast to the nose so you could get a normal looking fuse.

Maybe you could draw one up and show us?  maybe a short nose , short tail StuntWagon???

Regards
Randy

[RandySmith]

I used half a tank of fuel in the IC plane and a battery in the electric.  For 4 oz. of fuel to move the CG of a 64-oz. airplane an inch, the center of the tank would have to be 16" forward of the new CG, wouldn't it?

Hi Howard

Thanks I was curious if you were just going by the plan CG for an IC Impact, then measuring the EL one with battery..thanks you answered my question. I have not checked the spread sheet on the 4 ozs of fuel distance, but I do know a 1 ounce spinner washer moves it a bunch.  I have an average of less than 3 ounces of fuel in mine,
 and 5 3/4 oz doesn't seem to make a huge difference in the plane.  I need to go and measure my ship again, with a full load of fuel and see exactly how much it does move.

Randy

[RC Storick]

I am not sure if I will word this correct but..

People are concerned on how much more forward the CG is on electric instead of thinking maybe the IC is farther back than necessary. This is due to the heavyest part being farther forward. On a IC you move the CG back to get the turn rate you want but the farther back you move the CG you loose directional stability.

The next thing you have to negate and be able to attain is a gross weight that will allow a super turn. A light airplane with a farther forward CG is more stable for me than a heaver plane with a farther back CG to get the same turn rate.

I am sure with this last plane I built and learning what the package is capable of achieving in the feel of the aircraft the next evolution will even be better. Its not the turn rate I am looking for anyway its the feel.

[Doug Moon]

Its not the turn rate I am looking for anyway its the feel.

And.....that is exactly what you should be looking for. 

[Ted Fancher]

Hi Ted,
        when I said -
"concentrating the mass around the CG gives far more design flexibility and 'should' result in eventually a better model," you go on to say that you tried it and yet only moved mass rearward, and used that as a basis of criticism?

So I gather that you don't agree that centralizing the mass would be of benefit?

I do, and here we have the opportunity of using truly discreet components, with electric we can seriously use the greater mass of the fuel cell anywhere (within reason) as movable ballast (and this is what I truly got out of Roberts assertions) and that flexibility 'should' result in a better model.

So sure, just move the Battery back beneath the bell crank where the CG is located as long as the CG can be maintained by say perhaps reducing a corresponding amount of weight in the tail. (Just ruminating here outside of the above extreme example, keeping the moments intact and getting weight off the tail may be as simple as sacrificing looks and deleting anything further aft than the elevator hinge line except for the elevator itself of course.)

And how many models need lead in the tail to get the CG just right? Wouldn't it be nice to be able to keep both the lightest wing loading AND maintain the CG by simply shifting a necessary discreet component instead of adding a (possibly) unnecessary lump of lead?

And that is only covering pitch, what about using the battery mass to control roll for the vertical CG and tip weight?

Thanks.



Just being facetious, Chris.

One of the fascinating aspects of the amp/ohm breed is the flexibility (as you suggest) for experimentation the fixed mass hardware opens up.  Thus far, however, I've not seen any substantively different aerodynamic layouts that have turned judges' heads.

I've never been a person who championed the "zero ounce per square foot wing loading" as the pathway to stunt nirvana, believing that a balance between mass, lift and control response is more important.  The wing loading of major championship winning aircraft over the several decades of my involvement provides thought provoking, if not compelling, evidence for that perspective.

My gut feeling is that the damping provided by mass at the extremes will ultimately prove to be desirable for precision maneuvering by control systems other than those driven by complex intel directed inputs.  Thus far I've seen no substantial innovation in the layout of even the most competitive examples.  I'm the first to admit, however, that my current state of activity and, therefore, first hand exposure limits the landscape of my perspective.

I fly very little any more and only have a few hops on other peoples' electrics--none of which appeared to exhibit significant breakthroughs in terms of performance although most were "solid" stunt ships.

On the other hand I've judged  quite a bit since the "revolution" including a number of guys who have been "top guns" with whatever they fly.  Thus far I've not seen anything I consider to be breakthroughs in scoring as a result. 

It is, of course, early in the revolution.

[Ted Fancher]

Just a quick thought.

There are almost literally thousands of examples of CL aircraft that display exactly the parameters that Chris, Robert and others are discussing.  Mass and CG concentrated in almost exactly the same place with wing loadings as close to zero as is likely possible. 

They're called combat ships.  The fuel cell right on the CG and the motive force pushed back as close to it as possible.  The two units, power and fuel, probably comprise...what, Howard, 60% or more of the total TOGW?

Yup, they turn on a dime but pretty much need to have that streamer trailing behind to be even remotely capable of precision maneuvers.

Is this the future of stunt design envisioned by the event's leaders in the amp/ohm era?  Not trying to be snarky here, it's just the most logical destination of the train Sparky is conducting.

Ted

[RandySmith]

Just a quick thought.

There are almost literally thousands of examples of CL aircraft that display exactly the parameters that Chris, Robert and others are discussing.  Mass and CG concentrated in almost exactly the same place with wing loadings as close to zero as is likely possible. 

They're called combat ships.  The fuel cell right on the CG and the motive force pushed back as close to it as possible.  The two units, power and fuel, probably comprise...what, Howard, 60% or more of the total TOGW?

Yup, they turn on a dime but pretty much need to have that streamer trailing behind to be even remotely capable of precision maneuvers.

Is this the future of stunt design envisioned by the event's leaders in the amp/ohm era?  Not trying to be snarky here, it's just the most logical destination of the train Sparky is conducting.

Ted

Or..... a StuntWagon with the nose and tail moment shortened !! :-)

Randy

[RC Storick]

Is this the future of stunt design envisioned by the event's leaders in the amp/ohm era?  Not trying to be snarky here, it's just the most logical destination of the train Sparky is conducting.
Ted

True you are a NATS winner and I have no clue of what I am talking about but I will let you fly this combat ship with out a streamer and you tell me if it performs as I state. Rock solid level flight and combat turn with little input.

The next ship will have a faster control system in it and this one is already sped up as fast as I can make it with the 4 inch bell crank system already installed.

I need to get back to the field after last nights steaminf session. I had a slight twist in the inboard wing and some positive instance in the stab. After about 3 hours of steaming everything is straight and it should act much better. I was compensating for the wing with .5 oz of wing tip weight and I am hoping to take half of that out. But this will be a trial and error call. I might also need to remake the battery holder to move it up or down again. For me its hard to tell from the inside of the circle exactly whats happening with the airplane. But Fortunately I have a Gort eye in Ron OToole to spot these issues.

[Chris Wilson]

Or..... a StuntWagon with the nose and tail moment shortened !! :-)

Randy

Hi Randy,
                you must admit that is an extreme example mate.

I have seen an electric (glow converted design) model with the battery pushed back as far as the front of the bell crank and the owner mumbling to himself that he wished that he could push it back even further. And the model has the same moments as the ST 46 glow version and still flew very well as electric with a rearward battery pack.

Anyway, I see the point of maintaining the length of the moment arms for smoothness - I 'get' it.

But I can't help but feel that movable ballast must eventually be used as an aid - canard Blue Pants anyone?

[RandySmith]

Hi Randy,
                you must admit that is an extreme example mate.

I have seen an electric (glow converted design) model with the battery pushed back as far as the front of the bell crank and the owner mumbling to himself that he wished that he could push it back even further. And the model has the same moments as the ST 46 glow version and still flew very well as electric with a rearward battery pack.

Anyway, I see the point of maintaining the length of the moment arms for smoothness - I 'get' it.

But I can't help but feel that movable ballast must eventually be used as an aid - canard Blue Pants anyone?

Hi Chris  

LOL  maybe a little extreme, and it is good to have flexibility in designs, I just don't
 see much to gain in putting the battery at the CG on a conventional single engine stunt ship...maybe a twin would benefit?   or   yes  a  canard !!  


Randy

[RandySmith]

"The next ship will have a faster control system in it and this one is already sped up as fast as I can make it with the 4 inch bell crank system already installed."


Uhhggg  !   I would  really try to discourage  anyone who was trying to make really fast control setup in their stunt ships, This cause  many problem of control, stability and big problems in the wwind, as you would need to push the CG even farther forward, and run a very nose heavy ship..

Regards
Randy

[Serge_Krauss]

Posted from my wife's laptop. My computer has been fried for over a week now, with possible loss of 10 month's of some unbacked files, including some aero stuff. So...

'sorry I missed this thread. A couple thoughts though. Even though "We don't need no st-e-e-e-nking  math," a question - implied or otherwise - requiring an engineering solution will finally show that comparisons require it. 'doesn't matter how the topic is broached. Engineering topics have long been banished to "the south forty", to avoid these arguments that offend some. Regardless of ho a question - implied or otherwise - is phrased, it may just require a technical approach. The thread is good though, as long as feathers remain unruffled. So, yeah, insert the right data in those spreadsheets. Choice of the Main forum doesn't change that.

SK

[RC Storick]

Uhhggg  !   I would  really try to discourage  anyone who was trying to make really fast control setup in their stunt ships, This cause  many problem of control, stability and big problems in the wwind, as you would need to push the CG even farther forward, and run a very nose heavy ship..
Regards
Randy

That's what makes this Hobby go around I can run what I want. I know how to make it work. If I remember and I do Didn't Jimmy Castle win the Nat's with a plane and a 3 inch bell crank? I had 2 of his airplanes with that set up.

[Chris Wilson]

Hi Chris 

LOL  maybe a little extreme, and it is good to have flexibility in designs, I just DO see much to gain in putting the battery at the CG on a conventional single engine stunt ship...maybe a twin would benefit?   or   yes  a  canard !!   


Randy

Typo mate? 'Cause if its not I'm really confused as to where you stand!!

[RandySmith]

Hi Chris
yep a typo  I meant don't   

Randy

[RandySmith]

That's what makes this Hobby go around I can run what I want. I know how to make it work. If I remember and I do Didn't Jimmy Castle win the Nat's with a plane and a 3 inch bell crank? I had 2 of his airplanes with that set up.

Yes you are correct, you can run whatever you want, matters  not to me, I am just trying to give  good advice.....If you run a nose heavy plane however, you will need to fly huge amounts of practice, Like Jimmy did.
You will also have to be very careful in high winds so you do not have the plane pushed into the ground, like Jimmy did. THe high winds will loads the controls of that type setup and at some points you will  not be able to put enough control input to keep it out of the ground. That is a fact and it is just one you will need to be careful in winds.
 

Randy

[RC Storick]

Yes you are correct, you can run whatever you want, matters  not to me, I am just trying to give  good advice.....If you run a nose heavy plane however, you will need to fly huge amounts of practice, Like Jimmy did.
You will also have to be very careful in high winds so you do not have the plane pushed into the ground, like Jimmy did. THe high winds will loads the controls of that type setup and at some points you will  not be able to put enough control input to keep it out of the ground. That is a fact and it is just one you will need to be careful in winds.
 

Randy

I had many planes with 3 inch bell cranks in them. They work perfect! Bigger is not better it's just bigger.

The 4 inch bell crank came into being because of the heavy nose weight. Everyone thinking they need to over power the wight by leavering it. I don't have that feeling of all that concentrated weight. It was a trimming tool same with lowering the lead outs. You are right , I will never be right, You win but I will do it my way anyway.

[Chris Wilson]

And here's me thinking that bigger crank arms were about linearity of controls and less stress on linkages.

Didn't know about it battling CG issues.

[RandySmith]

The 4 inch bell crank came into being because of the heavy nose weight. Everyone thinking they need to over power the wight by leavering it. I don't have that feeling of all that concentrated weight. You are right , I will never be right, You win but I will do it my way anyway.

HI Sparky     I didn't win anything, just posting my opinion and advice ,as I said I was just giving advice, and Yes you can do it your way.
 I have zero problems with that, and neither does..or should, anyone else. As you say we all can do it  however we like.
 I have use 4, 4.5 and 4.75 inch bellcranks, They  did NOT go into my plane because of weight, nose weight, or heavy weight,
They went in because the planes were larger, and the had much larger control surfaces, they generated much more force, and the larger bellcranks went in for the same reason I used a  2 inch bellcrank in 1/2 A  ships, and some 15 size ships, the 35 to 40 ships got 3 and 3.5 inch bellcranks, the larger ships naturally got the larger cranks, because of the airplane size and loads, NOT because of  the nose weight or concentrated weight.
I have many 60 size stuntships that had 8 ounce 54s..., 8.2 ounce  64s,  8.5 ounce 71s. they have a lower amount of inertia in the nose than an EC  ship, but I still used the larger cranks.  This helps  keep the handle inputs reasonable.
You could, if you want use a 3.5 or a 3 inch bellcrank to help speed up your controls, that would be one way to accomplish that, however you do it, and it feels right, and performs well for you is all  that matters


Randy

[RC Storick]

And here's me thinking that bigger crank arms were about linearity of controls and less stress on linkages.

Didn't know about it battling CG issues.

Its the same with the 1.5 inch horns. Slow the controls down so you can run a aft CG. Levrage the nose weight. You can run a nose heavy airplane if the gross weight is light. For the last 20 years I have been building larger airplanes and I know what control inputs it takes on my airplanes. I choose to go in a diffrent direction now. Not giving advice to anyone. Please don't follow me I would rather be on this path alone. I know where I want to end up.